The present disclosure relates to an electrographic image forming apparatus, such as a printer, a copying machine, a facsimile or a multifunction peripheral.
An electrographic image forming apparatus includes an image carrier (for example, a photosensitive drum) carrying a toner image, a charging member (for example, a charging roller) electrically charging the image carrier, and a exposure device (for example, a LSU (Laser Scanning Unit)) irradiating a laser light to the image carrier. After the image carrier is uniformly electric-charged by the charging member, the laser light corresponding to image data is irradiated to the image carrier by the exposure device, thereby forming an electrostatic latent image to the image carrier.
In the image forming apparatus having such a configuration, in a case where temperature and humidity inside the apparatus become high and other cases, dew condensation may occur on the image carrier. In such a situation in which the dew condensation occurs on the image carrier, if charging of the image carrier by the charging member is attempted, larger current than normality flows between the image carrier and charging member to cause dielectric breakdown, and then, there is a possibility of causing image failure.
By contrast, there is a configuration supplying a toner (a developer) to a surface of the image carrier and removing this toner together with moisture on the surface of the image carrier when the temperature and humidity detected by a temperature and humidity sensor are equal to or more than predetermined values, thereby preventing the dew condensation to the image carrier.
In this configuration, in order to detect abnormality as the dew condensation of the image carrier, the temperature and humidity sensor is a requisite component. However, the temperature and humidity sensor, particularly a humidity sensor, is a relatively expensive part. Therefore, increase in cost is caused and it is difficult to meet request of price reduction of the apparatus. Further, in order to accurately detect temperature difference and humidity difference between the inside and outside of the apparatus by the temperature and humidity sensor, it is necessary to respectively arrange the temperature and humidity sensors to the inside and outside of the apparatus, and accordingly, there is a possibility of causing further increase in cost.